take a cab! this is not a good place to have a car (and not altogether necessary.) Downtown is a confusing mess of one way streets that not even the locals understand. If you stay in downtown, most things are within walking or cabbing distance anyway and you can always take the monorail to Seattle Center.
Seattle is an important gateway city to the Far East and the South Pacific, so if you're coming from there you'll probably find it's relatively cheap and easy to get to. The airport is very accessible from anywhere in the country, so visitors from anywhere should be able to get there easily. It's also serviced by interstates, but traffic is always a pain. Unfortunately public transportation here is very limited, so if you don't drive into the city you'll need to rent a car once you arrive.
The traffic here is always crowded and a real headache. However, it's really the only way to get around. Seattle is a relatively compact city when compared to others on the West Coast, but unfortunately there's no subway or el I know of (except the Monorail). I think people on this side of the country just love their cars too much! Anyway, it's worth dealing with the traffic to see the city, so just grin and bear it!
Getting here all depends on where you're traveling from! :-)
Traffic is unsightly in the Seattle area. Major thoroughfares, such as I-5 and 405 are often stop and go and bottlenecked for no clear reason. The best advice I can give is to be patient when driving anywhere here. Parking rates downtown can also be rather expensive (day rates of $5-15 for all day). The metro (bus) system is pretty easy to get around on and travels throughout Seattle and the east side (Bellevue area). There's the new Sounder train that travels from Tacoma/Kent/Auburn to Seattle, but my friends that ride that note that the times are limited (e.g., if traveling from Tacoma to Seattle in the morning, the last train leaves at something like 7am not necesssarily conducive to tourists). Travel from downtown to the Seattle Center (or vice-versa) on the monorail is a short trip (~90 seconds), but it beats the dozen blocks you'd have to otherwise walk. Taxis are also a fairly dependable way to get around. You'll find that most Seattlelites drive, bicycle, take metro, or walk in the downtown area.
Well once again Seattle is quite close to my home. It is a 3 hour drive for me, but for those of you wishing to fly in, there is Seatac Airport, and as I recall it is an International Airport. Trains and Ferries also stop here.
The bus system is good and within the Downtown core the fare is free. But if you go further the Driver will apparently hold you hostage on the bus till you show your fare.
Obviously the Taxi system is approachable and no warnings about this mode of transportation.
Traffic Trouble Spots: Unfortunately, there are many. Seattle's topography means that new roads and transit are very difficult to build; the lack of a rail system means that most people rely on their cars. Although horrible traffic jams can happen anywhere, anytime, there are some particular spots to be avoided:
I-5 southbound in the morning; the section between about NE 80th and the Ship Canal bridge is congested almost all the time.
SR-520 both ways, during the morning and evening rush hours. The westbound backup in the evenings is the worst.
I-405 between Renton and Bellevue (northbound in the mornings, southbound in the evenings).
I-405 between the I-5 interchange in Lynnwood, and the I-90 interchange. (northbound in the mornings, southbound in the evenings).
Montlake Blvd. through the UW campus. Southbound is usually worst. If there's a game at Husky Stadium, forget it.
From Vancouver, take Highway 99 all the way down to the border (Peace Arch) and take I-5 all the way south. You'll know you're close once you see the Space Needle.
Around downtown, walking or taking the bus is probably the way to go. Just pick up a free map from the tourist information center. Take the monorail to and from Seattle Center/downtown.
Don't go by car! Seattle is famous for it's terrible traffic jams. If you do drive, try to avoid peak hours. Driving around the city centre can be a bit confusing because, although the streets are laid out quite nicely, a lot of them are one way. It can be frustrating sometimes trying to get where you want to go.
Above is a link to trafic monitor on roads clear or most used times. plus once there they have links to more.